Formation Of Microvoids Research Articles

Formation of a Diffusion Barrier-Like Intermetallic Compound to Suppress the Formation of Micro-voids at the Sn-0.7Cu/Cu Interface by Optimal Ga Additions

Kirkendall micro-voids observed within ϵ-Cu3Sn or at the bulk Sn solder/Cu interface are undesirable imperfections in solder joints in electronic interconnections that significantly decrease the reliability of the joint. Recent studies have shown that micro-alloying could alter these interfacial reactions and improve the mechanical properties. In this study, we investigated the Cu-Ga-Sn phase equilibria at 200°C and the interfacial reactions between Cu substrate and Ga-doped Sn-0.7Cu solders with doping levels of 1.0, 2.0, and 3.0 wt.%. The assembled diffusion couples were isothermally annealed at 200°C for different time periods. The results showed that the thickness of the typical Cu-Sn IMCs (η-Cu6Sn5 and ϵ-Cu3Sn) progressively decreased along with the formation of the γ-Cu9Ga4 phase as the Ga-doping concentration was increased. The η-Cu6Sn5 and ϵ-Cu3Sn were completely suppressed and substituted by the γ-Cu9Ga4 phase when the Ga-doping concentration was 3 wt.%. More interestingly, the γ-Cu9Ga4 was the only IMC formed at the Sn-0.7Cu-3.0 Ga/Cu interface even when aging at 200°C for up to 1000 h, implying that the undesired defectiveness of Kirkendall micro-voids is possibly prevented by controlling the formation of the interfacial phase.

Hydrogen effects on electrochemically charged additive manufactured by electron beam melting (EBM) and wrought Ti–6Al–4V alloys

The hydrogen behavior in electrochemically charged electron beam melting (EBM) and wrought Ti–6Al–4V alloys with a similar β-phase content of ~6 wt% was compared. Hydrogenation resulted in the formation of microvoids, either adjacent to the surface or along interphases, their coalescence, and emanation of microcracks around them. The microstructure of the EBM alloy displayed a discontinuous arrangement of β-phase particles in the short-transverse direction, a smaller lattice constant of the β-phase, and more α/β interphase boundaries, making the EBM alloy more susceptible to hydrogen embrittlement. The hydrogenated alloys were composed of αH (hcp) and βH (bcc) solid solutions as well as δa (fcc) and δb (fcc) hydrides with lattice parameters that have not been reported before. These hydrides were transformed from the primary α-phase. No major microstrain difference was observed between the EBM and wrought alloys, either before or after hydrogenation. Microstrains in the α and β phases increased following hydrogenation; they were larger in the βH and δa phases compared to the αH and δb phases. A post-treatment that would increase the size of the β particles is suggested to improve the resistance of EBM Ti–6Al–4V to hydrogen-induced damage.

Microstructure, tensile properties and deformation behaviors of aluminium metal matrix composites co-reinforced by ex-situ carbon nanotubes and in-situ alumina nanoparticles

In this study, the origin of the high tensile ductility (>10% strain to fracture) of a new class of high-strength (yield strength >500 MPa) aluminium (Al) metal matrix composites (Al MMCs) co-reinforced by ex-situ carbon nanotubes (CNTs) and in-situ γ−Al2O3 nanoparticles was investigated. The microstructures of these unique Al MMCs prior to and post tensile testing were characterized in detail using high resolution transmission electron microscopy, in order to understand their response to tensile deformation. The pathways to the in-situ formation of γ−Al2O3 nanoparticles were identified and attributed to the high energy ball milling process, and the subsequent spark plasma sintering, which converted the amorphous Al-oxide into γ−Al2O3 nanoparticles. The in-situ γ−Al2O3 nanoparticles and Al matrix exhibited a semi-coherent interface, which led to a markedly increased dislocation density in the matrix around the nanoparticles during tensile deformation. These dislocations were precursors to microvoid formation and consequent dimples on further deformation. The co-operation of CNTs and γ−Al2O3 nanoparticles resulted in a long strain-softening stage and therefore excellent tensile ductility. The results suggested that the exploitation of hybrid reinforcement by ex-situ CNTs and in-situ nanoparticles can enable the fabrication of high-performance metal matrix composites.

Comparative Study of Microstructure, Physical and Mechanical Characterization of SiC/TiB2 Reinforced Aluminium Matrix Composite

Aluminium matrix composites impact greatly in modern trends for huge applications in the aerospace and automotive industry due to its better strength to weight ratio and temperature resistance capacity. This work investigated the effect on SiC and TiB2 powder reinforced aluminium matrix composite fabricated by stir casting. Stir casting is a widely used liquid state method of a fabrication technique for preparing metal matrix composite with the help of mechanical stirring. Density, tensile strength, hardness, and fracture analysis were done to observe the development of ceramic particle reinforced aluminium matrix composite. SEM analysis revealed the uniform distribution of reinforcement particles throughout the aluminium matrix. Universal tensile strength and micro hardness of aluminium matrix composite enhanced from 140 MPa to 182 MPa and 66 HV to 81 HV respectively due to the addition of particle reinforcement. The microstructural investigation from the fractured surface of tensile samples indicated ductile nature appeared in Al7075, Al7075/SiC, and Al7075/TiB2 composites due to nucleation and micro-voids formation.

Tensile deformation damage behavior of a high deformability pipeline steel with a ferrite and bainite microstructure

The work-hardening characteristics and deformation behavior of high deformability pipeline steel with a polygonal ferrite and bainite microstructure were studied in this paper. The high work-hardening ability of polygonal ferrite with 35% bainite (PF+35%B) dual phase sample contributed to its high tensile properties. Electron backscattered diffraction was conducted to analyze the mechanism of the micro-damage behavior. The results of kernel average misorientation and grain reference orientation deviation of the deformation microstructure revealed that the main deformation mechanism of the polygonal ferrite grain was slip with a number of slip systems. Dislocation rearrangement and a local orientation gradient caused by crystal rotation during sliding to cause the formation of micro-voids. The strain dispersion ability of the PF+35%B sample was better than that of the polygonal ferrite with 27% bainite (PF+27%B) dual phase sample. The risk of micro-voids nucleation and crack propagation were reduced to an improved plastic deformation ability for PF+35%B sample. The average Taylor factor (M) of the PF+35%B sample was higher than that of the PF+27%B sample, which indicated the grains of the PF+27%B sample was more liable to slip during deformation and yield under low stress. The evolution characterization of the micro-texture showed that the γ-fiber was more stable compared with the α-fiber, and the stronger γ-fiber may contribute to the improved plasticity.

Effect of Microstructural Features on the High-Cycle Fatigue Behavior of CoCrFeMnNi High-Entropy Alloys Deformed at Room and Cryogenic Temperatures

In this study, we examined the effect of deformation twins and dislocation cell structures on the fatigue properties of the CoCrFeMnNi high-entropy alloy using rotational bending fatigue tests. The dislocation cell structures and deformation twins were generated by prestraining the CoCrFeMnNi high-entropy alloy at room temperature (27 °C) and a cryogenic temperature (− 196 °C), respectively. To eliminate the effect of different material strengths on fatigue behavior, the tensile strengths of the specimens evaluated in the fatigue tests were kept similar by controlling the prestraining under room and cryogenic temperatures. The results of the rotational bending fatigue tests revealed that the CoCrFeMnNi high-entropy alloy prestrained at room temperature exhibited higher fatigue resistance and fatigue limit than the specimen prestrained at a cryogenic temperature. A small quantity of large micro-voids was formed at the triple junction of the grain boundaries in the specimen prestrained at room temperature, whereas a large quantity of small micro-voids was formed in the region where the deformation twins intersected the grain boundaries in the specimen prestrained at a cryogenic temperature. Therefore, it is concluded that the different aspects of micro-void formation affected the crack initiation and, consequently, the fatigue properties of the room and cryogenic temperature-prestrained alloys.

Modified friction stir clinching of 2024-T3 to 6061-T6 aluminium alloy: Effect of dwell time and precipitation-hardening heat treatment

This paper investigates the effect of dwell time and heat treatment on the modified friction stir clinched (MFSC) joint of AA2024-T3/AA6061-T6 Al alloys. The precipitation-hardening heat treatment method involves the combination of solution heat treatment (at 520 °C for 1 h) and aging (at 165 °C for 18 h) processes. The microstructure, failure load, hardness, and fracture behavior of the as-welded and heat-treated MFSC joints were investigated. TEM images show that re-precipitation of strengthening Al2CuMg and MgZn2 phases, dislocation density, and tangles are more pronounced in the heat-treated MFSC joint. A rise in dwell time increases the average grain sizes (1.39–6.65 μm), tensile-shear strength (101–133 MPa), and cross tension strength (59–88 MPa) of the MFSC welded 2024-T3/6061-T6 joints due to an upsurge in the in-process exposure time-induced heat input and inter-material flow. An increase in dwell time beyond 15 s is undesirable. It induces the formation of nugget cracks and micro-voids in the joints and an impaired joint failure load consequently ensues. Heat treatment processing further causes grain coarsening (2.48–9.15 μm) and improves the hardness (at the weld center), tensile-shear (146 MPa), and cross tension (102 MPa) failure strengths of the MFSC joints due to the re-precipitated strengthening phases.

EBSD analysis of microstructures and mechanical properties of softened zones in X60 reeled-pipeline welded joint after cyclic plastic deformation

The purpose of this study was to evaluate the microstructural evolution of softened zones after cyclic plastic deformation (CPD) and the effect of CPD on the mechanical properties of X60 reeled-pipeline welded joints. The results showed that the existence of softened zone caused the deformation to be mainly concentrated in this area during CPD process. The minimum hardness of softened zone was 18 HV less than the base metal (BM). As the global strain of the welded joints increased from the initial state without CPD to 5% strain, the kernel average misorientation of inter-critical HAZ related to the geometrically necessary dislocation slightly increased from 0.66° to 0.87°, resulting in a slight rise in hardness. Despite the presence of softened zones in HAZ, the location of tensile fracture was at BM, which was attributed to the combined effect of the work-hardening effect in softened zones, the groove type, and the constraining effect of the welded joint, regardless of the CPD strain levels. The decrease in ductility of welded joints was due to the stress concentration caused by dislocation pile-ups during the CPD process and then leading to the early formation of microvoids.

Evaluation of impact and hardness properties of Al 6063-AgNPs composites produced by stir cast technique

The effect of silver nanoparticles (AgNPs) on the mechanical and microstructural properties of aluminium 6063 alloy was investigated. Aluminium 6063 matrix was homogenously mixed with AgNPs impregnated with calcium carbonate at 2, 4 and 6% weight fractions. The mixture was used to produce refined samples through stir casting method. Measurement of impact strength and hardness property of the produced samples at ambient temperature was done by using Charpy impact and Brinell hardness testing machine in accordance with ASTM E23 and ASTM E384 respectively. The impact energy values (234-247 J) of all the samples with AgNPs/CaCO3 reinforcements were higher than the as-cast Al alloy (228 J) while the sample with 6% AgNp has the highest energy impact (247 J). Similarly, the hardness values (56.49-183.70 BHN) of all the samples with AgNPs/CaCO3 reinforcements were higher than the as-cast Al alloy (38.05 BHN) while the sample with 6% AgNPs has the highest (183.70 BHN). The magnitude of impact and hardness increased evidently with increase in percentage weight fraction of the AgNPs. The fracture images of the impact test samples revealed that the surface of AgNPs (CaCO3)-Al6063 composites were with dimples and there was a micro-void formation in CaCO3-Al6063 composite. The use of stir-casting technique influenced the homogeneity and microstructure of the AgNPs composites positively. The Al 6063-Ag nanocomposites possess better qualities in terms of impact energy and hardness, likewise can replace conventional aluminium alloy based on its performance.

A New Electron Backscatter Diffraction-Based Method to Study the Role of Crystallographic Orientation in Ductile Damage Initiation

The third generation of advanced high strength steels shows promising properties for automotive applications. The macroscopic mechanical response of this generation can be further improved by a better understanding of failure mechanisms on the microstructural level and micro-mechanical behavior under various loading conditions. In the current study, the microstructure of a multiphase low silicon bainitic steel is characterized with a scanning electron microscope (SEM) equipped with an electron backscatter diffraction detector. A uniaxial tensile test is carried out on the bainitic steel with martensite and carbides as second phase constituents. An extensive image processing on SEM micrographs is conducted in order to quantify the void evolution during plastic deformation. Later, a new post-mortem electron backscatter diffraction-based method is introduced to address the correlation between crystallographic orientation and damage initiation. In this multiphase steel, particular crystallographic orientation components were observed to be highly susceptible to micro-void formation. It is shown that stress concentration around voids is rather relaxed by void growth than local plasticity. Therefore, this post-mortem method can be used as a validation tool together with a crystal plasticity-based hardening model in order to predict the susceptible crystallographic orientations to damage nucleation.

Mechanisms of micro-voids formation caused by optical breakdown in KCl single crystals

The phenomenon of optical breakdown has been studied experimentally for KCl single crystals exposed to laser emission focused on the neodymium glass with modulated quality-factor, pulse duration 5·10-8 s, wavelength λ= 1054 nm, and pulse energy of the order 1 J in the regime of local intrinsic absorption of the laser emission by the single crystal. Evaluations of local heat flash energetic constituents and characteristic durations for both local area heating and relaxation processes and following comparison with experimental results have shown that the relaxation process takes place in two stages: the first is fast phasefollowed by crowdion mass transfer with shock wave participation, and the second is slow phase with participation also dislocation mass transfer. The energy losses for heat radiation and thermal conductivity are found to be by orders of value less than the absorption energy flux Iabs that provides fast local heating and plasma formation. From the viewpoint of the mechanics of continua the process under study where the pressure achieves value exceeding the theoretical strength limit for the time less 10-6 s, should be considered as explosion-like or shock process. The general scheme of plastic deformation arising from abovementioned estimations and observations is seemed as follows. In the beginning, under action of the shock wave the crowdions are generated which carry the substance from the high pressure area and move along close-packed atomic rows (<110> type directions in KCl crystals); the void is formed almost completely during the shock wave passing the relaxation zone crosssection. This time is of the order of τrel, i. e. 10-9…10-8 s. After falling temperature and pressure and vapor condensation into liquid, at the end of relaxation process, the void boundaries expand already under liquid melt pressure, and the mass transfer dislocation mechanism comes into action providing additionally some enlarging the void volume. This process continues also after stopping the laser emission, during the crystal cooling down to the melt crystallization in the void and formation of a pore with size observed.

Isothermal Diffusion Behavior and Surface Performance of Cu/Ni Coating on TC4 Alloy.

The poor surface performance of titanium alloys substantially limits their application in many fields, such as the petrochemical industry. To overcome this weakness, the Cu and Ni double layers were deposited on the surface of TC4 alloy by the electroplating method, and the isothermal diffusion process was performed at 700 °C to enhance the binding ability between Cu and Ni layers. The isothermal diffusion behavior and microstructure of the coating were systematically analyzed, and tribological property and corrosion resistance of the coating were also evaluated to reveal the influence of isothermal diffusion on the surface performance. It was shown that multiple diffusion layers appeared on the Cu/Ni and Ni/Ti interface, and that NixTiy and CuxTiy phases were formed in the coating with the increase of diffusion time. More importantly, Kirkendall diffusion occurred when the diffusion time increased, which led to the formation of continuous microvoids and cracks in the diffusion layer, weakening the surface performance of the Cu/Ni coatings. This paper unveils the relationship between the microstructure of the Cu/Ni coatings and isothermal diffusion behavior, providing guidelines in preparing high performance surface coatings.

Ductile fracture based joint formation mechanism during friction stir welding

Material movement during friction stir welding plays a significant role towards joint formation. However, there is little clarity on periodic or continuous nature of material movement. The objective of this work is to understand the mechanism of joint formation during friction stir welding, by investigating the periodic formation of a cavity and if formed, cavity's role towards the joint formation. A two dimensional numerical methodology is developed to capture the material flow around the tool pin. The plastic limit load model is used to predict the formation of microvoids, growth and coalescence. Friction stir welds are made with AA 1050 at different tool travel speeds, for same tool rotation frequency across experiments. Computed tomography of friction stir welded samples is performed to study the size and morphology of the discontinuities. The chemical constituents, size and distance between inclusions are determined from scanning electron microscopy and energy dispersive spectroscopy of the as-received AA 1050. The numerical model suggests that the stress and strain during friction stir welding of AA 1050 is sufficient for nucleation and growth of the voids at the inclusion sites. Further the voids coalesce to form a cavity in all the cases. The incoming material fills the cavity per revolution. However, in some cases the cavity is partially filled which leads to the discontinuities in the weld. For the welds with discontinuities, the area of unfilled cavity is predicted to be larger in advancing side as compared to retreating side. The discontinuity size increases as the travel speed increases. The tunnel discontinuity is predicted by super-positioning of the discontinuities formed over consecutive passes along the feed direction. The discontinuity size and shape trends compare well against the experimental observations. This work would be helpful towards developing strategies for detecting and mitigating the discontinuities formed during friction stir welding.

Thermal Stability and Hardness Studies of Ge Doped Se–Te Glassy Alloys

The amorphous glassy alloys Se82 – xTe18Gex (x = 0, 4, 8, 12, at %) was synthesized using melt quench technique. Thermal stability was examined with the help of various parameters such as Dietzal parameter, Hruby parameter, Saad and Poulin and Lu and Liu parameters. Vicker hardness was obtained from Vicker hardness tester and other related thermo-mechanical properties such as volume of micro-voids, energy formation of micro-voids and modulus of elasticity were calculated.

On the transition of fracture toughness in metallic materials with thickness: An atomistic viewpoint

From thick to very thin specimens, fracture toughness of metallic materials peaks out before hitting much lower value compared to the constant plane strain fracture toughness value obtained using standard fracture mechanics testing of thick specimens. Understanding this behavior is essential for improving reliability of small-scale metallic devices currently being used for various critical applications. To understand this behavior, it is essential to study the process of dislocations emission and interaction at the crack front and its variation with specimen thickness. To this end, atomistic fracture simulations of pre-cracked single crystal FCC metal (Nickel) specimens representing both thick and thin specimens are performed. At first, stress-state dependent single crystal yield function based on the generalized Schmid-law is associated with the dislocation emission process at the crack front for both thin and thick specimens. Fracture simulations are then performed on single crystal specimens representing different thickness cases. Due to low stress triaxiality prevailing throughout the thickness of thin specimens, dislocation interaction with each other inside the specimen and then with the specimen surface leading to wedge-shaped groove formation on opposite surfaces at crack front is found to be the responsible mechanism of crack propagation in thin specimens. This mechanism provides enhanced fracture toughness to thin specimen compared to thick specimen in which crack propagation is based on high stress triaxiality at the core of the crack front making formation of microvoids and their coalescence as a dominant mechanism of crack propagation. The dislocation configurations generated at the crack front for thick and thin specimens are also studied and the mechanisms for dislocation multiplication in thin specimens compared to thick specimens are highlighted.

Investigation of local tensile strength and ductility properties of an X100 submerged arc seam weld

Tensile testing is the most common method to determine the mechanical properties of a weld joint, yet the local tensile properties can be different from the global properties when stress localization occurs. In the current study, Digital Image Correlation was used to explain the difference in local and global tensile behavior in different sections of a submerged arc specimen. Tensile tests are used to compare the base metal and weldment properties of a two-pass submerged-arc welded X100 pipe steel in terms of strength and ductility. The base metal exhibits superior tensile strength compared to specimens machined from the second pass (Pass 2) or the overlap weld region spanning between Passes 1 and 2, corresponding to the reheated heat affected zone. Both cross-weld tensile specimens fractured in the fine grained heat affected zone (FGHAZ). Although the overlapped tensile specimen achieved higher global strain compared to the Pass 2 weld specimen, it sustained lower local strain, which promoted fracture in the HAZ. In addition, the overlapped tensile specimen exhibited a higher degree of strain hardening. The martensite-austenite (MA) microconstituents in the FGHAZ of Pass 2 contained higher carbon than the MA in the overlapped FGHAZ, which led to increased MA hardness as measured by nanoindentation. A higher fraction of MA with a finer spacing in the FGHAZ of the overlapped HAZ zone provides higher strength and strain hardening but lower ductility. The tensile fracture was dominated by void formation from the hard MA/ferrite interfaces in all tensile specimens, and so an increased fraction of MA led to accelerated microvoid coalescence, and reduced ductility in the overlapped HAZ specimens. In-situ strain monitoring technology via Digital Image Correlation was used to identify the potential fracture location during tensile test. X-ray tomography clearly revealed microvoid formation and coalescences of voids.

Deformation and failure mechanisms of Ti–6Al–4V as built by selective laser melting

The ability to create complex geometries with tailored material properties has brought interest in using additive manufacturing (AM) techniques for many industrial applications. However, further understanding of the complex relationship between AM process parameters, microstructure, and resultant properties is critical for the widespread use of metal AM. In this study, selective laser melting (SLM) is used to print Ti–6Al–4V. Tensile tests with concurrent microstructural analysis using electron backscatter diffraction, electron channeling contrast imaging, and digital image correlation are performed to understand the damage and its relation to the microstructure of Ti–6Al–4V after SLM processing. We find that the as-printed Ti–6Al–4V shows hierarchical microstructures, consisting of primary, secondary, and tertiary α' martensite. This hierarchical structure is formed as a result of cyclic heat treatment during the layer-wise SLM process. Upon tensile deformation, strain localization within primary α' martensite results in microscopic ductile micro-void formation and coalescence, as well as macroscopic brittle fracture. In addition to localization inside primary α', surface steps at the boundaries of these high aspect ratio grains are formed which reveal the contribution of interfacial plasticity to the overall deformation of the material.

Effect of morphology alteration on mechanical properties and fracture toughness of polypropylene/polyamide 6/ethylene polypropylene diene monomer graft maleic anhydride (PP/PA6/EPDM-g-MA) reactive ternary blends

Morphology, mechanical properties and fracture behavior of polypropylene/polyamide 6/ethylene polypropylene diene monomer graft maleic anhydride (PP/PA6/EPDM-g-MA) ternary blends containing various amounts of the EPDM-g-MA rubbery phase (from 0 to 9 wt%), with special attention to the structure–property relationships through the core–shell morphology development, were studied. The fracture surface, deformation micro-mechanisms and mechanical properties of the blends were examined using field emission scanning electron microscopy technique, tensile and impact tests, respectively. The fracture properties were characterized in detail by the linear elastic fracture mechanics method. The fracture energy (GC), fracture toughness (KIC) and impact strength were improved monotonically up to some EPDM-g-MA content, above which the characteristics were appreciably enhanced. These results were attributed to an alteration of this morphology from dispersion of PA6/EPDM-g-MA core–shell particles at low EPDM-g-MA contents to the aggregated structure of core–shell particles at higher EPDM-g-MA contents. The micro-void formation via activation of internal cavitation or debonding of the rubbery phase was found to be responsible for the stress whitening phenomenon that occurred during the impact fracture process and, hence, increased impact toughness.

Effect of microstructural aspects in the heat-affected zone of high strength pipeline steels on the stress corrosion cracking mechanism: Part I. In acidic soil environment

Microstructures consisted of bainite/ferrite matrix and varied distribution of martensite-austenite (M-A) constituent in the heat-affected zone of X100 pipeline steel were simulated, and their effect on stress corrosion cracking (SCC) mechanism in acidic soil environment were investigated. The results showed that microstructure characteristic, especially distribution of M-A constituent, had large effect on SCC sensitivity. Micro-galvanic effect, stress/strain concentration and hydrogen involvement facilitated formation of microvoids at M-A/matrix interface, which could promote initiation and propagation of SCC microcracks through microvoids coalescence. SCC microcracks also preferred propagating along upper bainite laths whereas acicular ferrite and quasi-polygonal ferrite could inhibit the crack propagation.

Experimental investigations in the intermetallic and microvoid formation in sub-200 °C Cu–Sn bonding

This paper reports the intermetallic growth and microvoid formation in the Cu–Sn layers, which were annealed at low temperatures (sub-200°C) for durations varying from 120 to 1440 min. A 10 µm thick tin was electrodeposited on copper samples. Both Cu6Sn5 and Cu3Sn IMCs were formed and had a non-uniform scalloped shaped profile but with different scallops sizes. Void growth was studied at three different locations, i.e., the Cu–Cu3Sn interface, within the Cu3Sn, and at the Cu3Sn–Cu6Sn5 interface. The void size in these locations increased with increasing annealing durations and temperatures due to the coalescence of nearby voids. The void fraction at the Cu–Cu3Sn and Cu3Sn–Cu6Sn5 interfaces was observed to decrease, whereas the void fraction within the Cu3Sn IMC increased with increasing annealing durations. The largest voids were seen at the Cu–Cu3Sn interface, while the highest void fraction was found within the Cu3Sn IMC. The overall void size and void fractions for all experimental conditions were always smaller than 3 µm2 and 1.44 µm−1, respectively. The obtained results can be used in the hermetic packaging of MEMS devices performed at sub-200 °C. Processing at these low temperatures result in reduced thermo-mechanical stress and also eliminate the molten tin squeezing-out from the bonding zone, which is a known issue in Cu–Sn solid–liquid inter-diffusion bonding performed at temperature > 232 °C.